The purpose of this study was to investigate the therapeutic benefit of local Glycosaminoglycan polysulfate (GAGPS) injections in the treatment of chronic epicondylalgia. The study was conducted as a prospective, placebo-controlled double-blind trial. Sixty patients with a typical history of pain for at least 3 months who attended two private orthopaedic clinics in Stockholm received 50 mg GAGPS or placebo injections, one injection a week, for five weeks. The main outcome measures were the patients' evaluation of pain in connection with daily activities with a visual analogue scale and the number of treatment failures. The follow-up period was six months. The difference in reduction of painscore (VAS) ranging between 11.1 percentage units at the half-year follow-up and 20.9 percentage units 2 weeks after the treatment period is clinically good. The number of treatment failures in the GAGPS treatment groups at the 6 week follow-up was only 4 (13%) compared with 12 (40%) of the placebo treated patients. At the half-year follow-up 5 of those who received GAGPS had experienced a recurrency. The recurrency rate is thus smaller than most of those reported in controlled studies with corticosteroids. In the GAGPS treated group 13 patients reported on local pain after some injections, 2 cases combined with local haematomas, compared with 5 cases of local pain in the placebo group. The results confirm previous good results of GAGPS injection therapy in subchronic and chronic peritendinitis.